Generally, an electrothermal transducer (heater) of a recording head mounted on a recording apparatus acting on an ink-jet system and a driving circuit thereof, as disclosed in U.S. Pat. No. 6,290,334, for example, is formed on the identical substrate using a semiconductor process technique. In addition to the driving circuit, there has been proposed a configuration of the recording head having: a digital circuit or the like which detects a state of a semiconductor substrate such as a temperature of a substrate is formed on the identical substrate; ink supply ports around the center of the substrate; and heaters facing each other at such positions as to sandwich each of the ink supply ports.
FIG. 1 is a view illustrating a frame format of circuit blocks and ink supply ports of this kind of ink-jet recording head substrate (head substrate). FIG. 1 illustrates six ink supply ports 111 on the semiconductor substrate of the head substrate 110. FIG. 1 illustrates only the circuit block provided for the ink supply port 111 on the left for convenience and illustration of the circuit blocks provided for the other five ink supply ports 111 is omitted. As illustrated in FIG. 1, the heaters 112 are disposed in an array manner at such positions as to face each other, sandwiching each of the ink supply port 111 therebetween. The circuit blocks (driving circuits 113) for selectively driving the heaters 112 are disposed so as to be provided for the heaters 112. Pads 114 for supplying power and signals to the heaters 112 and driving circuits 113 are arranged at one end of the semiconductor substrate 110.
FIG. 2 is a view illustrating a frame format of a circuit configuration and signal flows of the driving circuits 113 in FIG. 1. Signals including image data and the like applied to the pads 114 are inputted into a block selection circuit 203 (constituted of a shift register, mainly) and a time-division selection circuit 202 (constituted of decoders, mainly) which constitutes an internal circuit through an input circuit 201. An example illustrated in FIG. 2 shows that the inputted image data is converted into a time-division selection signal by the time-division selection circuit 202. The time-division selection signal is transmitted to each of heater driving blocks 1 to 8 (204). The block selection circuit 203 produces a block selection signal for selecting the heater driving blocks 1 to 8 based on an image data signal synchronous with a synchronizing signal (clock) used to input an image data. The heater driving block selected by the block selection signal drives the heater in accordance with the time-division selection signal. That is, a heater driven by AND of the block selection signal and the time-division selection signal is decided.
FIG. 3 illustrates a detail configuration of a heater driving block 204. The heater driving block 204 includes heater driving MOS transistors 306, level conversion circuits 304 and heater selection circuits 305 disposed so as to be provided for the heater 112 arranged in an array manner. The heater driving MOS transistors 306 function as a switch for turning on and off the energization of the heater 112. A block selection signal 302 from the block selection circuit 203 and a time-division selection signal 303 from the time-division selection circuit are inputted into an AND gate of the heater selection circuit 305. Accordingly, if both of the two signals 302, 303 are active, an output of the AND gate becomes active. An output signal of the AND gate is level-converted by a level conversion circuit 304 into such a power voltage (second power voltage) that a voltage amplitude of the signal is higher than a driving voltage (first power voltage) from an input circuit to the heater selection circuit 305. The level-converted signal is applied to a gate of the heater driving MOS transistor 306. The heater 112 connected to the heater driving MOS transistor 306 to which the signal is applied to the gate is energized current and driven. The reason the level conversion circuit 304 makes a level conversion into the second power voltage in the heater driving block 204 is that the voltage applied to the gate of the heater driving MOS transistor 306 is increased to decrease on-resistance thereof, thus passing electric current through the heater with high efficiency.
FIG. 4 illustrates an internal circuit of a general level conversion circuit 304 and a peripheral circuit thereof. The level conversion circuit 304 is divided into a circuit section 304a operating on the first power voltage and a circuit section 304b operating on the second power voltage. A heater selection signal 401 as an output from the heater selection circuit 305 is inputted into an inverter 412a (constituted of a PMOS transistor 410 and a NMOS transistor 411) operating on the first power voltage. The inverter 412a produces an inversed logic signal of the heater selection signal 401 and applies the signal to gates of a NMOS transistor 414 and a PMOS transistor 413 operating on the second power voltage. An inversion signal of the inverter 412a is inputted into an inverter 412b for the second inversion. An output signal of the inverter 412b is applied to gates of a NMOS transistor 416 and a PMOS transistor 415 operating on the second power voltage. The circuit section 304b produces a signal having an amplitude value of the second power voltage for switching the heater driving MOS transistor 306 in accordance with these input signals and inputs the signal into the gate of the heater driving MOS transistor 306.
As described above, the circuit of the ink-jet recording head substrate includes the circuit block operating on the first power voltage having the voltage amplitude of an input signal and the circuit block operating on the higher second power voltage to be applied to the gate of the MOS transistor for controlling a current flowing the heater (hereinafter referred to as heater current). That is, the ink-jet recording head substrate has a configuration so as to be controlled and driven by two types of power voltages, namely a first and a second power voltages, and so as to convert the signal amplitude of the first power voltage into the signal amplitude of the second power voltage by the level conversion circuit.
The first and the second power voltages are power voltages supplied to the respective recording head substrates from a printer body. In starting power supply, the order of application of the second power voltage and the heater power voltage after application of the first power voltage is required to be observed. This is because application of the second power voltage and heater voltage under no application of the first power voltage may cause an output of the level conversion circuit 304 to be unstable and the heater driving MOS transistor 306 to be ON, thus continuing to energize heater current. To achieve such a power input order, measures are required to be taken in the printer body, which causes a cost increase.